Things could have been much worse. In December, a blizzard in the Northeast wiped out more than 10,000 flights over three days, and a mid January storm led airlines to cancel nearly 9,000 flights.

Friday's shutdown occurred late enough in the day that many of the canceled flights were the last planes out for the day, said Henry Harteveldt, an airline analyst with Forrester Research. On a Monday morning, the results could have been catastrophic.

"It happened as a lot of the airline was going to sleep for the night," Harteveldt said.

That doesn't mean affected travelers were happy.

"I'm just amazed at how catastrophic the failure was," said Jason Huggins, 35, who was trying to fly home to Chicago after a week working at his software company's San Francisco headquarters. "All the computer screens were blank, just showing the United logo."

Huggins paid $1,200 to book one of the last three seats left on an American Airlines flight home.

Social workers Penny Nord­strom, 57, and Emily Schaefer, 42, who were trying to get home to Spirit Lake, Iowa, from Cancun, Mexico, said their delays started with a computer problem at midday Friday in Mexico.

"We're way past 24 hours now," Nordstrom said at noon Saturday before she boarded a rebooked flight from Chicago O'Hare International Airport to Detroit for a connection to Sioux Falls. She expected to get home about midnight but hoped her travel insurance would offer some compensation.

United spokesman Charles Hobart said late Saturday afternoon that the airline didn't expect to cancel any more flights this weekend due to the computer problems, though delays might continue.